There are many communication systems in operation today, including virtually all of today's selective call systems, that utilize frequency modulation (FM) for addressing, and for data and voice transmission. The current communication subscriber units, e.g., selective call devices, utilize sophisticated receiver architectures, and today's selective call systems utilize well known and established signaling formats. The current receiver architectures and signaling formats have been optimized to provide both high receiver sensitivities and excellent battery saving capabilities.
In many metropolitan areas, many selective call systems are operated at, or near, the maximum system capacity, in both the number of subscribers that can be accommodated, and the message transmission time that is available. Such selective call system operation has resulted in reduced customer satisfaction due to extended times required to access the selective call system, and also due to extended delays in message delivery due to equally extended selective call system message transmission queues. At present, this need is being met by increasing the data rate of the protocol used or increasing the latency time by requiring the selective call devices to battery save longer.
To further aggravate the problem, the limited radio spectrum available worldwide or nationwide makes it challenging to provide seamless communication to and from the selective call devices. It has become necessary to equip the selective call devices with frequency synthesizers to enable them to scan or select among the frequencies within the available selective call spectrum when the selective call devices are roaming or has lost their signal. However, because there are a limited number of available selective call frequencies, no significant system expansions can be achieved or expected although there is a significant increase in the message length and the number of subscribers.
Thus, what is needed is a selective call system that can improve message delivery without the need for any addition of dedicated selective call frequency allocation.